Increased risk of various types of cancer in people with autoimmune diseases (AIDs) has long been hypothesized by many researchers. One of the proposed biological mechanisms for this relationship lies in the concept of immunosurveillance, in which a healthy immune system will remove aberrant cells produced during cell replication to prevent them from coming malignant cells and progressing to clinical cancer. Among individuals with AIDs, this regulation process is likely impaired, accounting for increased cancer risk in this population. Development of cancer related to drugs used to treat particular autoimmune diseases, such as rheumatoid arthritis, is also thought to contribute to the excess risk. We propose a retrospective cohort study utilizing existing data to study patterns of cancer development among people hospitalized for rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Sjogren's syndrome (SS), and scleroderma. We will take advantage of having three large, population-based data sets at our disposal to examine this issue. Specifically, we propose to link data from the 1991-2000 California Patient Discharge Dataset to California Cancer Registry (CCR) and California mortality data in order to identify individuals with AIDs and follow them forward in time to assess the development of cancer. We will use standardized incidence ratios to compare the observed cancers to expected numbers, based on calendar, site, age, and sex specific incidence rates in the California population. We will also make comparisons of subsets of the RA and SLE cohorts to specific groups of hospitalized patients in order to evaluate the differential effects of treatment with cytotoxic agents. A subset of the RA cohort who is also hospitalized for joint replacement surgeries will be compared to a group with osteoarthritis (OA) who are hospitalized for the same surgeries. We are using hospitalizations for joint replacement surgeries as a marker for more advanced RA. In addition, the former group is routinely treated with cytotoxic agents, while the latter is not. Women with SLE who are hospitalized for deliveries will be compared to those hospitalized for deliveries who do not have lupus. By selecting women of childbearing age, we hope to gain information on cancer risk in a subgroup of women with SLE who have less severe disease, a difficult group to identify in a hospitalized population. This study is exploratory in nature; we hope to be able to draw conclusions about the feasibility of using the linked data to identify a cohort of individuals with autoimmune disease (AID) who develop cancer. The results of this type of study also have potential implications for developing recommendations around cancer screening and surveillance of particular patient populations.